The present invention relates to cutoff saws, and more particularly to vertical band cutoff saws.
A wide variety of cutoff saws has been developed for cutting off plates, merchant bars, extruded and rolled shapes, and the like. In particular, band cutoff saws are particularly useful for cutting off gates and sprues of brass, bronze, and iron castings and for cutting off high-speed and stainless steel. The kerf or width of the cut in a band saw is relatively small with a consequent small loss of expensive cut material
One particularly effective vertical band cutoff saw is that sold as Model GV1NE by Tannewitz, Inc., of Grand Rapids, Mich., the assignee of the present invention. This saw includes a rail-mounted drive carriage supporting the band. The material to be cut is held stationary, while the saw band is carried through the material by the carriage riding on the rails. The saw carriage is driven at a selected constant feed rate through the material.
It is known in the art that a saw element, such as a band, will have the longest life if the load on the band is generally uniform during cutting. Too great a load, and even too light a load, are detrimental to the blade's life causing excessive wear and dulling. With constant-speed feed drive, the load on the saw band can vary greatly as it passes through material. Variations in band load are created partly by "hard spots" and/or "soft spots" in the material. Other variations in band load are occassioned by materials having nonuniform cross sections throughout the length of the cut, such as rods and pipe. Constant feed rates in band cutoff saws therefore result in varying band loads which detract from the life of the band.
In general, methods and apparatuses have been developed for estimating and/or approximating the band load and controlling the cutting element speed and/or feed rate in response thereto in an attempt to provide a uniform band load. However, these methods and apparatuses are either not particularly accurate or not adaptable to vertical band cutoff saws.
For example, circular cutoff saws include a circular rotating blade and a drive mechanism for carrying material through the rotating blade. At least one prior artisan has sensed the saw motor speed and regulated the feed rate in response thereto. As the rpm decreases, it is assumed that the load on the blade has increased; and the feed velocity of the material is reduced to decrease the blade load. Conversely, if the load on the saw blade decreases, the motor speed increases; and the feed rate is increased to increase the blade load. However, the control delay in this arrangement is unacceptably slow for many applications. This is particularly so in band saws wherein the momentum of the wheels carrying the band is relatively large.
In horizontal band saws, the blade is oriented generally horizontally, and the saw frame supporting the band travels downwardly under gravity to carry the band through the material. The downward force of the saw frame can be monitored to provide an estimation of the band load. For example, a relatively large downward force or weight indicates that the band is lightly loaded, while a relatively light downward force indicates that the saw band is heavily loaded. Using this force information, the descent rate of the saw frame can be controlled to maintain a relatively constant band force. Examples of such horizontal cutoff saw control systems are illustrated in U.S. Pat. No. 4,358,974, issued Nov. 16, 1982, to Sakurai, entitled METHOD AND APPARATUS FOR CONTROLLING THE FEEDING OF A BANDSAW BLADE OF HORIZONTAL BAND SAW MACHINES; U.S. Pat. No. 4,357,848, issued Nov. 9, 1982, to Sakurai et al, entitled METHOD AND APPARATUS FOR CONTROLLING THE FEEDING OF A BANDSAW BLADE OF HORIZONTAL BANDSAW MACHINES; U.S. Pat. Nos. 4,016,787 and 3,991,644, issued Apr. 12, 1977, and Nov. 16, 1976, respectively, to Sugimoto, entitled METHOD FOR CONTROLLING THE CUTTING FEED SPEED OF A SAW FRAME OF BAND-SAWING MACHINE OR SIMILAR MACHINE. However, this control utilizing the "apparent weight" of the frame is not usable in vertical cutoff saws wherein the direction of the cut is generally perpendicular to the force of gravity.
Another prior artisan has incorporated load sensors into the saw band guides of a vertical band saw. The force exerted on the guide by the band is monitored, and the feed rate of the material is regulated to maintain a relatively uniform load as detected by the load sensors. Examples of this construction are illustrated in U.S. Pat. Nos. 2,815,561 and 2,754,567, issued Dec. 10, 1957, and July 17, 1956, respectively, to Crane, entitled AUTOMATIC FEED CONTROL APPARATUS FOR MACHINE TOOLS. However, the incorporation of the load sensors into the relatively compact, "dirty", and hostile environment of the saw band guides can often result in inadequate performance and a requirement for frequent servicing.